Functional roles of tree neighbourhood diversity and complexity in the face of global changes

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Great progress has been made in the last 20 years towards understanding the key roles of biodiversity and complexity in the healthy functioning of both natural and man-made ecosystems. However, very little to no research has evaluated how both biodiversity and complexity of spatial patterns interact to affect ecosystem functioning under various environmental conditions, particularly in forests. This research program aims to investigate how tree diversity and spatial complexity patterns can affect many key ecosystem processes and how this new knowledge could be used to better manage our natural world, from our most popular urban parks, agricultural crop, garden and managed forests to conservation areas set aside in remote areas in the face of global changes. More precisely, this project tackles 2 novel and broadly complementary questions: (1) how does tree diversity (richness, functional and phylogenetic) interact with complex spatial patterns and various environmental stresses (e.g. drought, soil fertility, extreme weather) to affect ecosystem functioning, resilience and productivity, and (2) what are the functional cost/benefits for trees to live alone vs. in complex neighbourhoods with the aim of disentangling when and how positive species interactions becomes as important as competition in treed communities.I will make use of a world unique network of high-density tree diversity experiments that I have helped initiate in the USA, Canada and Europe. By varying experimentally the density, diversity and spatial distribution of trees under various soil and environmental conditions, this project will test novel hypotheses regarding (1 the role of non-native organisms in diverse and complex communities, (2) the potential role of facilitation in non-stressful environments, and (3) the effects of complex spatial patterns in increasing complementarity of resource uses in treed communities.